Transducer operated switches



NWv 10 vv 1970 J. R. ASHLEY ETAL Y TRANSDUCER QPERATED SWITCHES f Filed May 1 1969 Ja/.w /Qs/f/.EY Ken/very J," #Nasr/ANN B7 MMX L ffl" ,4f/6,

Umted States Patent O U.S. Cl. 307-117 2 Claims ABSTRACT F DSCLOSURE A transducer-controllable ON/OFF switching mechanism comprises a primary changeover switch biassed to one condition and changeable by the transducer to the other condition, a second changeover switch in circuit with the first switch and an electric motor driving a rotor carrying alternate main ON and OFF switch actuators with, between each two adjacent main actuators, a second switch actuator for changing over the second switch, and parallel connections between the rst and second switches, whereby on any change of the first switch the motor starts, a main actuator effects a main switching operation and thereafter a second actuator changes the second switch to stop the motor.

This invention concerns transducer operated switches, by which is meant switches operated in response to changes of electric current generated or controlled by transducers. By change of electric current is meant change from at least a minimum value at which a switch would be caused to operate in one sense to a maximum value at which the switch would be caused to operate in the reverse sense. The minimum value may be zero. The actual range of the change of current generated or controlled bythe transducer may extend beyond said minimum and/ or said maximum value. Also the change of current so generated or controlled may be progressive or it may be a sudden change. The exact nature of the current change depends upon the form of the transducer and/or the change of a controlling condition which determines the response of the transducer.

Typical transducers are photoconductive and thermoconductive transducers whereby, in general, the rate of change of current generated or controlled thereby may be progressive as the environmental condition progressively changes, but may be in the nature of a sudden change when that condition changes suddenly. Another form of transducer is typified by a tuned oscillator, such as a tuning fork or a piezoelectric device, usually used in combination with an amplifier and responsive to a signal received over such means as a radio link or wave guide, or a conductive line, eg., a coaxial line, or a pilot line, or as a signal imposed upon a line having also another conducting function, e.g., a high frequency signal imposed on a 50 cps. power cable or on a component of an audiofrequency tele-transmission line.

The invention concerns transducer operated switches for operation in response to a wide variety of transducers, as exemplified above. Furthermore, it concerns switches adapted to respond to transducers in close proximity to the switches or at a distance. A switch so controlled may for instance be part of a remotely actuatable centralised electrical load control system involving a tuned oscillator type of transducer. In another arrangement the transducer may be a photo-conductive cell and the switch a component of a street or other lighting controlling circuit.

It is typical of switch-controlling transducers that, due either to the nature of the transducer or to other considerations, the current primarily generatedor controlled by the transducer or the extent to which it can be amplified is not always great enough to operate a high current rating switch with acceptable efficiency.

It has been indicated above that a typical application of transducer operated switches is in the automatic control of lighting circuits by photoconductive cells; for convenience, the invention will be described, and its primary object stated, with reference to that form of control, but it will be apparent from the foregoing and following remarks that the invention is not restricted to switches controllable only from photoconductive cells.

The usual procedure for controlling a high current rated switch by a photoconductive cell is to use the cell to control the current flow in the energising coil of a relay or the heater of a bimetallic switch. In both cases severe limitation is imposed on the size of the load which can be controlled by the small dissipation of the photoconductive cell. For instance, a relay for switching a load of about 15 amperes at 240 volts A.C. would have an energising coil rating of about 40 m./a., thus making it unsuitable for use in a direct current series circuit with a photoconductive cell typically dissipating about 1 watt at about 35 C.

To enable higher current rated switches to be controlled it has been necessary to use cascade circuits of relays aucl/ or bimetallic switches. In the case, for instance, of a two-relay cascade, the primary relay has to have low contact pressure rating in view of the small amount of energy available, from the photoconductive cell, for actuating the relay. The second relay, which has to operate the switch, introduces limitation because of its inductive reactance. In the case of a cascade arrangement of which at least the primary element is a bimetallic switch, the effective heater current must be low enough not to overload the photoconductive cell; this again imposes limitations on the switching capacity of the device and also, since low contact pressure is likely to occur for a period prior to opening of the primary contacts, contact burning or frying is likely if the current density is too high.

The object of this invention is to provide anew transducer operated switch with which the above mentioned disadvantages will not be associated.

In accordance with the invention, a transducer operable switch comprises a primary single-pole changeover switch operable by an actuating element which is energisable directly or indirectly by a transducer, and an electric motor having its energising circuit connected to the primary switch by a second similar switch so that the motor energising circuit can be completed and opened by the second switch in each condition of the primary switch, and a rotor driven by the motor carries alternate ON and `OFF switch actuators and, between each two adjacent switch actuators, a limit-switch actuator for changing over the condition of the second changeover switch.

An embodiment of the invention will be described by way of example and with reference to the accompanying circuit diagram.

Between two poles I., N of an electric supply system are connected in series a photo-conductive cell 1, i.e., the transducer, and a low current consumption heater coil 2, i.e., the actuating element, of a bimetallic changeover switch, i.e., the primary switch, comprising two fixed contacts 3, 5.and an intermediate movable contact 4 which is connected to the supply pole N. In the nonenergised condition of the bimetallic switch its contacts 3, 4 are in engagement and in its energised condition its contacts 4, 5 are in engagement.

The energising winding 1S of a synchronous motor is connected between the supply pole L and the movable contact 8 of a changeover limit switch, which may be a microswitch, of which the two switch contacts 6, 7 are separately connected to the iixed contacts 5, 3 respectively of the bimetallic changeover switch, to provide alternative connections between the two switches.

The synchronous motor drives a rotary tappet plate 16, in a clockwise direction as seen in the diagram, through a reduction gear 15a. The tappet plate 16 carries an even number of spaced tappets, four being illustrated, comprising the switch actuators and consisting of ON tappets 12 alternating with OFF tappets 11. Between each two adjacent tappets the plate 16 carries an end-sequence striker plate or limit switch actuator 10. The main switch mechanism 17 to be actuated has adjacent to the tappet plate 16 appropriate ON and OFF levers, represented diagrammatically by an ON lever 14 and an OFF lever 13, for actuation by the ON tappets 12 and OFF tappets 11 respectively.

The striker plates are adapted to engage a limit switch trip 9 which is so coupled to the changeover limit switch that each time the trip 9 is engaged by a striker plate the condition of the limit switch is changed over.

The operation of the device is as follows. It will be assumed that initially the main switch to be operated is ON, and that the heater coil 2 is unenergised with the contacts 3, 4 of the bimetallic primary changeover switch in mutual engagement and also the second limit switch in the condition with its contacts 6, 8 in mutual engagement. If now the heater coil 2 is energised by the photo cell 1, the primary switch changes over, thereby separating contacts 3, 4 and closing contacts4, 5 to complete an energising circuit through the contacts 6, 8 of the second changeover switch to the motor winding 15. The tappet plate 16 is now turned by the motor so that an OFF tappet 11 engages the OFF lever 13 to open the main switch and thereafter, with continued drive by the motor, an end-sequence striker plate 10 engages the trip 9 to change over the condition of the second changeover or limit switch, which is equivalent to opening the energising circuit for the motor winding 15 since the contacts 3, 4 of the bimetallic primary switch are disengaged from one another. When at a subsequent time the heater coil 2 ceases to be energised by the photocell 1, the condition of the bimetallic primary switch again changes to separate its contacts 4, 5 and brings its contacts 3, 4 into mutual engagement to close againa circuit through the second changeover switch to the motor winding 15. The tappet plate 16 now turns until an ON tappet 12 engages the `ON lever 14 to close the controlled main switch and thereafter an end-sequence striker plate 10 engages the trip 9 to change over the condition of the second changeover switch and thus again interrupt the energising circuit for the motor winding l15.

Thus once either an ON tappet 12 or an OFF tappet 1-1 has operated the main switch it is followed by an operation upon the second changeover or limit switch, by an end-sequence plate 10, in the sense to cut olf the current supply to the motor and leave the device in an anticipatory state in readiness for the next main switching operation to be eiected at the next change of state of the iirst changeover switch.

Whereas by the previously known two-relay form of control circuit a 30-ampere main switch appears to be about the maximum size to be controllable by photoconductive cells, by the use of a separate contactor, the invention provides for the control of switches of a much higher rating, eig., 80 amperes in one control. The synchronous motor represents only a small load, typically 2 watts, which is well within the capacity of the bimetallic switch.

As an indication of the positive advantages of transducer-operable switches constructed in accordance with the invention, and given lby way of example only, it is pointed out that due to the small switching requirements of the bimetallic primary switch (2 watts approximately) the power consumption of this device may be limited to some 300 mw. This, coupled with the fact that the motor only operates during a switching action, which could be as little as 1 minute per action or up to say l2 minutes per action, according to the preset delay for which the operating tappets are adjusted, provides a very low consumption unit. The average for a time switch is about 2.5 watts and for existing photocell controls about 4.5 watts maximum with an average of about 3 watts. The consumption of the new device is calculated at about 400 mw. over any 24-hour period or about 1/eth of the consumption of an existing time switch and about 1/sth of that of an existing photo-switch design.

Although, by way of example, the invention has been described for control by a photocell, it will be appreciated that the transducer may be of any other convenient form, for instance a tuned oscillatory device, with or without an amplified output, as previously described in this specification. Also the invention is not restricted to an arrangement in which the primary switch is a bimetallic switch; for instance it may be any form of changeover relay of wrich the actuating element would usually Ibe a solenoid. We claim:

1. A transducer-controllable electric ON/ OFF Switching mechanism, consisting of an electric motor driven rotor carrying ON switch actuators alternating with OFF switch actuators to drive said actuators in circular paths, main switch actuating means extending into said paths for engagement in succession by an ON switch actuator to close a main switch and an OFF switch actuator to open said main switch, a primary single-pole changeover switch biased into one state and having a primary switch actuating element which is energisable by a transducer to change over said primary switch to its other state, limitswitch-actuators carried by, and alternating with the ON and OFF switch actuators on, the rotor so that there is a limit-switch-actuator between each two adjacent switch actuators, a second single-pole changeover switch having a second actuating element extending into the path of the limit-switch-actuators to be actuated by each limitswitch-actuator in turn to successively change the state of the second switch first in one sense by a limit-switchactuator and next in the opposite sense by the next limitswitch-actuator, the motor being connected in series with said primary and second switches between electric power input terminals, and parallel connections extending between said primary and second switches to provide` in one condition of said primary switch that the series circuit is complete in one condition of said second switch and incomplete in the other condition of said second switch and in the other condition of said primary switch that the series circuit is incomplete in said one condition of said second switch and is complete in said other condition of said second switch, whereby any change of condition of said primary switch will start the motor and thereupon, in succession, a switch actuator will operatively engage the main switch actuating means and a limit-switch-actuator will operatively engage the second actuating element to change the condition of said second switch to stop the motor.

2. A transducer-controllable electric ON/ OFF switching mechanism as claimed in claim 1, wherein said primary switch is a bimetal thermal switch, and the primary switch actuating element is an electric heater for said 'bimetal thermal switch.

References Cited UNITED STATES PATENTS 2,300,857 11/1942 Ankenman 307-117 X 3,350,581 1071967 Stein 307-117 3,356,908 12/1967 Mitchell et al 307-117 X ROBERT K. SOHAEFER, Primary Examiner H. I. HOHAUSER, Assistant Examiner 

